Specificity of the commonly used enzymatic assay for plasma cholesterol determination

Case Report: Next Generation Sequencing in Clinical Practice–A Real Tool for Ending the Protracted Diagnostic Odyssey

We reported a case of sitosterolemia, which is a rare genetic disease, characterized by increased plant sterol absorption and great heterogeneity of clinical manifestations. Our patient was initially referred to the lipid clinic due to high cholesterol levels and premature cardiovascular disease. Diagnosis of familial hypercholesterolemia was established in accordance with the Dutch Lipid Clinic Network criteria. Next-generation sequencing was later performed, which revealed a nonsense mutation in the ABCG8 gene, which led to the diagnosis of sitosterolemia. The aim of our report is to demonstrate, how genetic testing helped to make the correct diagnosis and to explain many of the patient's health problems, which etiology remained unclear for many years.

Recent advances in ABCG5 and ABCG8 variants

PURPOSE OF REVIEW

In this review, we summarize the genetics and mechanisms of sitosterolemia and sterol trafficking, and provide an update on the understanding of the prevalence of ABCG5 and ABCG8 variants and their role in human disease.

RECENT FINDINGS

Defects in ABCG5/G8 result in the accumulation of xenosterols. It had been previously thought that near total LoF of one of the proteins was required to cause pathology. However, recently there was the first report of a patient with Sitosterolemia who was heterozygous for mutations in both genes. Moreover, large population studies have demonstrated the even simple heterozygous carriers are associated with altered lipid profiles and cardiovascular risk. Broader screening has added to the rapidly growing list of gene variants indicating that the prevalence of ABCG5/G8 variants is higher than previous thought, especially in patients with hypercholesterolemia.

SUMMARY

These findings support a strategy of measuring xenosterol levels in patients with hypercholesterolemia to screen for ABCG5/G8 variants, and then tailoring treatment with a sterol absorption inhibitor, like ezetimibe, where indicated. Xenosterol trafficking affects remnant clearance and maybe pathogenically linked to the increased risk of atherosclerosis.

Genetics of Familial Hypercholesterolemia: New Insights

Familial hypercholesterolemia (FH) is one of the most common monogenic diseases, leading to an increased risk of premature atherosclerosis and its cardiovascular complications due to its effect on plasma cholesterol levels. Variants of three genes (LDL-R, APOB and PCSK9) are the major causes of FH, but in some probands, the FH phenotype is associated with variants of other genes. Alternatively, the typical clinical picture of FH can result from the accumulation of common cholesterol-increasing alleles (polygenic FH). Although the Czech Republic is one of the most successful countries with respect to FH detection, approximately 80% of FH patients remain undiagnosed. The opportunities for international collaboration and experience sharing within international programs (e.g., EAS FHSC, ScreenPro FH, etc.) will improve the detection of FH patients in the future and enable even more accessible and accurate genetic diagnostics.

Recent Developments of Useful MALDI Matrices for the Mass Spectrometric Characterization of Lipids

Matrix-assisted laser desorption/ionization (MALDI) is one of the most successful “soft” ionization methods in the field of mass spectrometry and enables the analysis of a broad range of molecules, including lipids. Although the details of the ionization process are still unknown, the importance of the matrix is commonly accepted. Both, the development of and the search for useful matrices was, and still is, an empirical process, since properties like vacuum stability, high absorption at the laser wavelength, etc. have to be fulfilled by a compound to become a useful matrix. This review provides a survey of successfully used MALDI matrices for the lipid analyses of complex biological samples. The advantages and drawbacks of the established organic matrix molecules (cinnamic or benzoic acid derivatives), liquid crystalline matrices, and mixtures of common matrices will be discussed. Furthermore, we will deal with nanocrystalline matrices, which are most suitable to analyze small molecules, such as free fatty acids. It will be shown that the analysis of mixtures and the quantitative analysis of small molecules can be easily performed if the matrix is carefully selected. Finally, some basic principles of how useful matrix compounds can be “designed” de novo will be introduced.

Methodological considerations for the harmonization of non-cholesterol sterol bio-analysis

Non-cholesterol sterols (NCS) are used as surrogate markers of cholesterol metabolism which can be measured from a single blood sample. Cholesterol precursors are used as markers of endogenous cholesterol synthesis and plant sterols are used as markers of cholesterol absorption. However, most aspects of NCS analysis show wide variability among researchers within the area of biomedical research. This variability in methodology is a significant contributor to variation between reported NCS values and hampers the confidence in comparing NCS values across different research groups, as well as the ability to conduct meta-analyses. This paper summarizes the considerations and conclusions of a workshop where academic and industrial experts met to discuss NCS measurement. Highlighted is why each step in the analysis of NCS merits critical consideration, with the hopes of moving toward more standardized and comparable NCS analysis methodologies. Alkaline hydrolysis and liquid-liquid extraction of NCS followed by parallel detection on GC-FID and GC-MS is proposed as an ideal methodology for the bio-analysis of NCS. Furthermore the importance of cross-comparison or round robin testing between various groups who measure NCS is critical to the standardization of NCS measurement.

Effects of high performance inulin supplementation on glycemic status and lipid profile in women with type 2 diabetes: a randomized, placebo-controlled clinical trial

BACKGROUND

Type 2 diabetes mellitus, as a noncommunicable disease, is the main public health challenge in the 21st century. The prevalence of diabetes mellitus adjusted for the world population in Iran was 8% until the year 2010.Lipid levels are considered as important parameters to be evaluated, as high serum lipid levels are often reported as a complication in patients with diabetes mellitus.It is claimed that functional foods may improve complications of diabetes mellitus, so this study was designed to evaluate the effects of high performance inulin on glycemic status and lipid profile of women with type 2 diabetes.

METHODS

The study was a randomized controlled clinical trial. Forty-nine type 2 diabetic females (fiber intake <30g/d, 25<BMI<35 kg/m2) were divided into two groups. Patients in the intervention group (n=24) received 10g/d inulin and patients in the control group (n=25) received 10g/d maltodextrin for 8 weeks.Glycemic status and lipid profile indices were measured pre and post intervention. Data were analyzed using SPSS software (verision11.5). Paired, unpaired t-test and ANCOVA were used to compare quantitative variables.

RESULTS

Supplementation with inulin caused a significant reduction in FBS (8.50%), HbA1c (10.40%), total cholesterol (12.90%), triglyceride (23.60 %), LDL-c (35.30 %), LDL-c/HDL-c ratio (16.25%) and TC/HDL-c ratio (25.20%) and increased HDL-c (19.90%). The changes for the control group parameters were not significant at the end of study.

CONCLUSION

Inulin may help to control diabetes and its complications via improving glycemic and lipid parameters.

Soy protein, genistein, and daidzein improve serum paraoxonase activity and lipid profiles in rheumatoid arthritis in rats

In this study, we investigated the effects of genistein, daidzein, and soy protein on paraoxonase and arylesterase activity, malondialdehyde (MDA) levels, and lipid profiles of arthritic rats in vivo and the results were compared with that of dexamethasone. Seventy-two female Sprague-Dawley rats were divided into six groups: healthy control, animals with collagen-induced arthritis (CIA), CIA-soy protein (7 g/kg)-treated rats, CIA-genistein (20 mg/kg)-treated animals, CIA-daidzein (20 mg/kg)-treated rats, and CIA-dexamethasone (1 mg/kg)-treated rats. Rheumatoid arthritis was induced using collagen type II and the treatments were carried out by daily gavages feedings for 50 days. The paraoxonase activity in serum was measured spectrophotometrically using paraoxon and phenylacetate as substrates. Serum MDA and lipids levels were determined using enzymatic colorimetric methods. Arthritis-induced decreases in paraoxonase and arylesterase activity was restored after treatment with soy protein and isoflavones (P<.05). MDA concentrations were lower after treatment with all tested compounds. However, only soy protein could partially improve the lipid profile.

Biological evaluation of a siliconized analog of clofibrate (silafibrate) in rodents

Silicon is the element very similar to carbon, and bioactive siliconized compounds have therefore received much attention. Siliconization of a compound enhances its biological activities. In the present study the hypolipidemic effect and toxicity of clofibrate and its siliconized analog, silafibrate, were compared. The experiments were performed in hypercholesterolemicWistar rats. Animals received high fat diet with 62.75% normal chow, 2% cholesterol, 0.25% cholic acid, 15% lard oil, 10% wheat flour and 10% sucrose.Silafibrate(40 mg/kg/day) produced a predominant reduction in the serum levels of total cholesterol (28.4%, p < 0.001), triglycerides (62%, p < 0.0001) and low-density lipoproteins (27%, p < 0.001) being more effective than the reference drug clofibrate (20%, 40%, 14.5%; p < 0.05). Similarly, it increased the total antioxidant levels in serum by 40% (p < 0.05). Simultaneously, treatment with silafibrate also reduced the malondialdehyde(MDA) concentration by 41% (p < 0.05). LD50 of silafibrate, given orally,was greater than 2000 mg/kg body weight inalbino mice while LD50 for clofibrate was calculated to be 1220 mg/kg. Thirty-day subacute toxicity was also evaluated with oral daily dose at 25, 50 and 100 mg/kg body weight in Wistarrats. No significant changes in body weight, food intake, behavior, mortality, hematology, blood biochemistry, vital organ weight were detected. The results of this study indicate that the effectiveness and safety of thehypolipidemic drug, clofibrate, were enhanced remarkably by replacing chlorine atom in its phenoxy ring with trimethylsilyl.

Effects of orange juice and hesperetin on serum paraoxonase activity and lipid profile in hyperuricemic rats

INTRODUCTION

Hypouricemic, antioxidant and xanthine oxidase inhibitory effects of orange juice and hesperetin have been already indicated. The objective of this study was to investigate the effects of orange juice and hesperetin on paraoxonase and arylesterase activity and lipid profile of hyperuricemic rats.

METHODS

Forty eight male Wistar rats were divided into 8 equal groups of healthy control, healthy+orange juice, healthy+hesperetin, healthy+allopurinol, hyperuricemic control, hyperuricemic+orange juice, hyperurice-mic+hesperetin and hyperuricemic+allopurinol. Hyperuricemia was induced using potassi-um oxonate (250 mg/kg ip). The treatments were carried out by daily gavage of 5 ml/kg orange juice, 5 mg/kg hesperetin and 5 mg/kg allopurinol for 2 weeks. Paraoxonase activi-ty in serum was measured spectrophotometrically using paraoxon and phenylacetate as substrates. Serum lipids levels were determined using enzymatic colorimetric methods.

RESULTS

Hyperuricemia-induced reduction of paraoxonase and arylesterase activity was restored after treatment with orange juice and hesperetin (p<0.05). The effect of both treatments on lipid profile was marginal and only orange juice could significantly increase the levels of HDL-C.

CONCLUSION

Supplementation of orange juice and hesperetin could restore paraoxonase and arylesterase activity in hyperuricemic rats. Orange juice could also partially improve the lipid profile. These effects could have major implications with respect to the prevention of cardiovascular disease in hyperuricemic patients. However, more studies are needed in future investigations.

Long-term efficacy and safety of ezetimibe 10 mg in patients with homozygous sitosterolemia: a 2-year, open-label extension study

OBJECTIVE

To assess the long-term efficacy and safety profile of ezetimibe 10 mg/day in patients with homozygous sitosterolemia.

METHODS

This was an extension of a multi-centre, randomised, double-blind, placebo-controlled base study in which patients with homozygous sitosterolemia and plasma sitosterol concentrations > 5 mg/dl were randomised 4 : 1 to ezetimibe 10 mg/day (n = 30) or placebo (n = 7) for 8 weeks. Patients who successfully completed the base study with > 80% compliance to study medication were eligible to enter two, successive, 1-year extension studies in which ezetimibe 10 mg/day was administered in an open-label manner. Patients remained on their current treatment regimen (e.g. bile salt-binding resins, statins and low-sterol diet) during the base and extension studies. Patients had to be off ezetimibe therapy for > or = 4 weeks prior to entering the first extension. Efficacy and safety/tolerability parameters were evaluated every 12 and 26 weeks in the first and second years respectively. The primary efficacy end-point was mean percentage change in plasma sitosterol from baseline to study end for the cohort of patients (n = 21) who successfully completed the second extension study.

RESULTS

Treatment with ezetimibe 10 mg/day led to significant mean percentage reductions from baseline in plasma concentrations of sitosterol (-43.9%; p < 0.001), campesterol (-50.8%; p < 0.001), low-density lipoprotein (LDL) sterols (-13.1%; p < 0.050), total sterols (-10.3%; p < 0.050) and apolipoprotein (apo) B (-10.1%; p < 0.050). No significant changes from baseline were observed for lathosterol, high-density lipoprotein sterol, triglycerides or apo A-1. Maximal reductions in sitosterol and campesterol occurred within the first 52 weeks of treatment and were sustained for the duration of the study. For LDL sterol, total sterols and apo B, maximal reductions were achieved early (by weeks 4 or 16) and waned slightly through the remainder of the study. Overall ezetimibe 10 mg was well tolerated.

CONCLUSION

In patients with homozygous sitoserolemia, long-term treatment with ezetimibe 10 mg/day for 2 years was effective in reducing plasma plant sterol concentrations with an overall favourable safety and tolerability profile.

Decreased nicotinic receptors and cognitive deficit in rats intracerebroventricularly injected with beta-amyloid peptide(1-42) and fed a high-cholesterol diet

To investigate whether the changes in nicotinic receptors (nAChRs) and in learning and memory associated with Alzheimer's disease (AD) are influenced by both beta-amyloid peptide (Abeta) and cholesterol in vivo, we examined the effects of intracerebroventricular injection of Abeta(1-42) and/or a high-cholesterol diet on brain levels of nAChRs and learning and memory in rats. The levels of nAChR subunit proteins and the corresponding mRNA were measured by Western blotting and RT-PCR, respectively; and learning and memory were evaluated with the Morris Water Maze examination. Injection of Abeta(1-42) resulted in deposition of this peptide, activation of astrocytes, decreased levels of the alpha7 and alpha4 protein subunits of the nAChR, and elevated expression of alpha7 mRNA, as well as impaired learning and spatial memory. A high-cholesterol diet activated astrocytes and, more importantly, potentiated the toxic effects of Abeta on nAChR subunit levels and on learning and memory. These findings may be highly relevant to the mechanisms underlying the cognitive deficits associated with AD.

Dietary phytosterols reduce probucol-induced atherogenesis in apo E-KO mice

We have previously shown strong pro-atherogenic effects of probucol in apolipoprotein E-knockout (apo E-KO) mice. The aims of the present study were to investigate whether (a) dietary phytosterols reduce probucol-induced atherogenesis and (b) beneficial interactions exist between these agents. Male apo E-KO mice fed with an atherogenic diet supplemented with phytosterols or probucol or their combination for 14 weeks. Single therapy with either phytosterols or probucol resulted in a 25% reduction in plasma total cholesterol (TC) concentrations as compared to the control group. The effects of the combination therapy were more profound (60% reduction). While phytosterols reduced atherogenesis by 60%, probucol caused an increase of 150% in atherogenesis. Addition of phytosterols to probucol substantially reduced pro-atherogenic effects of probucol. This was associated with improved high density lipoprotein (HDL) concentrations. The ratio of TC to HDL cholesterol was markedly reduced in the combination therapy group as compared to the probucol-treated group. A strong positive association between the ratio of TC to HDL cholesterol and the extent of atherosclerotic lesions was observed. The coronary arteries of the probucol-treated group showed various stages of atherogenesis from infiltration of monocytes into intima to complete occlusion of the vessel by atheromatous lesions. Such pathological findings were not observed in the combination therapy group. Approximately 40% of the mice in the probucol-treated group and 10% of the animals in the combination therapy group developed skin lesions. Further studies warrant the investigation of the underlying mechanisms of the observed beneficial interactions between dietary phytosterols and probucol.

Abcg5/Abcg8-independent pathways contribute to hepatobiliary cholesterol secretion in mice

The ATP-binding cassette (ABC) half-transporters ABCG5 and ABCG8 heterodimerize into a functional complex that mediates the secretion of plant sterols and cholesterol by hepatocytes into bile and their apical efflux from enterocytes. We addressed the putative rate-controlling role of Abcg5/Abcg8 in hepatobiliary cholesterol excretion in mice during (maximal) stimulation of this process. Despite similar bile salt (BS) excretion rates, basal total sterol and phospholipid (PL) output rates were reduced by 82% and 35%, respectively, in chow-fed Abcg5(-/-) mice compared with wild-type mice. When mice were infused with the hydrophilic BS tauroursodeoxycholate, similar relative increases in bile flow, BS output, PL output, and total sterol output were observed in wild-type, Abcg5(+/-), and Abcg5(-/-) mice. Maximal cholesterol and PL output rates in Abcg5(-/-) mice were only 15% and 69%, respectively, of wild-type values. An infusion of increasing amounts of the hydrophobic BS taurodeoxycholate increased cholesterol excretion by 3.0- and 2.4-fold in wild-type and Abcg5(-/-) mice but rapidly induced cholestasis in Abcg5(-/-) mice. Treatment with the liver X receptor (LXR) agonist T0901317 increased the maximal sterol excretion capacity in wild-type mice (fourfold), concomitant with the induction of Abcg5/Abcg8 expression, but not in Abcg5(-/-) mice. In a separate study, mice were fed chow containing 1% (wt/wt) cholesterol. As expected, hepatic expression of Abcg5 and Abcg8 was strongly induced (fivefold and fourfold) in wild-type but not LXR-alpha-deficient (Lxra(-/-)) mice. Surprisingly, hepatobiliary cholesterol excretion was increased to the same extent, i.e., 2.2-fold in wild-type mice and 2.0-fold in Lxra(-/-) mice, upon cholesterol feeding. Our data confirm that Abcg5, as part of the Abcg5/Abcg8 heterodimer, strongly controls hepatobiliary cholesterol secretion in mice. However, our data demonstrate that Abcg5/Abcg8 heterodimer-independent, inducible routes exist that can significantly contribute to total hepatobiliary cholesterol output.

Examining the interaction of apo E and neurotoxicity on a murine model of ALS-PDC

Epidemiological studies have shown a positive relationship between cycad flour consumption and the development of the neurodegenerative disorder, amyotrophic lateral sclerosis – parkinsonism – dementia complex (ALS-PDC). Apolipoprotein E (apo E) allele variations have been associated with genetic susceptibility in neurodegenerative diseases, including ALS-PDC. We have studied cycad toxicity in a mouse model of ALS-PDC with a particular interest in its impact on the central nervous system (CNS) in both apo E knock-out (KO) mice and their wild-type (WT) counterparts. Behavioral motor tests, motor neuron counts, and immunohistochemical staining in brain and spinal cord, as well as routine histological examinations on internal organs, were performed to evaluate cycad toxicity. Plasma cholesterol levels were also measured before and during the study. Cycad treatment was associated with higher levels of plasma cholesterol only in apo E KO mice; increased levels of plasma cholesterol did not result in increased athero genesis. Cycad-fed wild-type mice developed progressive behavioral deficits including ALS-PDC-like pathological outcomes, while cycad-fed apo E KO mice were not significantly affected. Cycad-fed wild-type mice had shorter gait length measurements along with higher active caspase-3 levels in the striatum, substantia nigra, primary motor cortex, and spinal cord as compared with corresponding controls. These changes were associated with decreased labeling for glutamate transporter 1B and tyrosine hydroxylase activity levels. No evidence of cycad toxicity was observed in internal organs of either wild-type or apo E KO mice. Our data demonstrate that apo E KO mice are less susceptible to cycad toxicity, suggesting a role for apo E as a possible genetic susceptibility factor for some forms of toxin-induced neurodegeneration.Key words: apolipoprotein E, amyotrophic lateral sclerosis (ALS), ALS-parkinsonism dementia complex (ALS-PDC), parkinsonism, dementia, neurodegeneration, glutamate transporter, sterol, sterol glucoside.